1. Field of the Invention
The present invention relates to telephone systems, and more particularly to abbreviated dialing systems for Touch Tone telephone instruments.
2. Description of the Prior Art
Equipment capable of providing an abbreviated dialing feature typically is installed as an attachment to a subscriber telephone instrument or is accomplished by a computerized system located at a telephone central office. At the present time, a relatively small percentage of telephone central offices have purchased the computer equipment required to provide an abbreviated dialing capability for its subscribers. Thus there is a substantial market for abbreviated dialing systems which can be either purchased or leased by a subscriber to provide an abbreviated dialing capability for one or more of his telephone instruments.
U.S. Pat. No. 3,993,877 (Sendyk) discloses an abbreviated dialing system which is inserted in series with a subscriber's telephone line to provide an abbreviated dialing capability for a single pulse dialed telephone instrument. With further circuitry a second telephone instrument can be coupled to the system. The electronic structure of this system requires that the DC loop current and dial tone to the telephone instrument be interrupted at certain times. The system apparently has the flexibility to add a second telephone extension, but cannot serve more than two instruments. When a second instrument is added, circuitry which is able to designate the controlling telephone must be added.
Another somewhat different abbreviated dialing system is disclosed in U.S. Pat. No. 3,917,911 (Lesher). The Lesher reference discloses a system which upon receiving a pulse dial input designating an apartment dweller's residence retransmits a full sequence telephone number corresponding to the telephone number of the selected apartment dweller. The circuit is extremely limited since it is only able to provide this service from a single non-standard telephone instrument and is incompatible with multi-frequency or Touch Tone dialing signals.
U.S. Pat. Nos. 4,053,718 (Dervaux), 4,010,330 (Shio) and 3,105,121 (Field) disclose various abbreviated dialing systems which are incorporated within a single telephone instrument. Devices of this type are structurally limited to serving only a single telephone instrument and are thus limited in their function and service with a subscriber having a plurality of telephone instruments. If the subscriber desires to have access to the abbreviated dialing system, he must utilize one of the specially equipped instruments and none other.
The following United States patents disclose other less relevant abbreviated dialing systems which are either located at a telephone central office or are limited in that they can serve only a single telephone instrument: U.S. Pat. Nos. 4,007,333 (Marheine), 3,325,602 (Truby), 3,334,190 (Jenkins et al), 3,194,890 (Haskins) and 3,702,905 (Gil).